Method and apparatus for limiting energy at ignition of an electric arc

Abstract

In order to ensure a safe operation of a welding device, in which low voltage pulses (P(U1)) occurring on a low voltage side (21) of the welding device (100) are converted into high voltage pulses (P(U2)) occurring on a high voltage side (22) of the welding device (100), an arc is ignited between an electrode (17) and a workpiece (W) during an ignition operation and / or a no-load operation using the high voltage pulses (P(U2)), in which ignition operation and / or no-load operation a time window (T) is provided extending from a start time (Ta) to an end time (Te), during which time window (T) an ignition energy value (E) occurring at the electrode (17) is determined and compared with an energy limit value (G), in the event of which energy limit value (G) being exceeded an action (A) is triggered in order to prevent further high voltage pulses (P(U2)) in the time window (T).

Description

TECHNICAL FIELD

[0001] The invention relates to a method for safe operation of a welding device, wherein low-voltage pulses occurring on a low-voltage side of the welding device are converted into high-voltage pulses occurring on a high-voltage side of the welding device, wherein during an ignition operation an arc is ignited at an electrode using the high-voltage pulses. The invention furthermore relates to an energy limiting unit for a welding device having a low-voltage side and a high-voltage side, and to a welding device comprising a low-voltage source designed to generate low-voltage pulses on the low-voltage side, and comprising a conversion unit for converting the low-voltage pulses generated on the low-voltage side into high-voltage pulses on the high-voltage side for igniting an arc between an electrode and a workpiece on the high-voltage side, and comprising an energy limiting unit according to the invention. BACKGROUND

[0002] In some welding devices low-voltage pulses are converted into high-voltage pulses. The high-voltage pulses mostly contain an energy of 100 microjoule (μJ) to 10 joule (J) and are used during an ignition process for igniting an arc at an electrode. After the ignition process the actual welding process is carried out when the arc is burning, wherein here of course much greater energy values occur at the electrode compared to the ignition operation. The document AT 413 953 B discloses a method for contactless ignition of an arc using ignition pulses combined into a pulsed beam. Thereby the energy value output during the ignition process is kept essentially small. The document WO 2012 / 162582 A1 describes a monitoring of the energy value output to a workpiece during a welding process. SUMMARY

[0003] It is the task of the invention to propose a method for safe operation of a welding device and an energy limiting unit for a welding device.

[0004] The task is solved in this way according to the invention that in the ignition operation a time window is provided which extends from a start time to an end time, wherein during the time window the ignition energy value occurring at the electrode is determined and compared with an energy limit value, in the event of which an action is triggered in order to prevent further ignition energy at the electrode in the time window. Furthermore the task is solved by means of an energy limiting unit, wherein the energy limiting unit comprises an energy determining unit which is designed to determine the ignition energy value occurring at the electrode during the time window which extends from the start time to the end time in the ignition operation of the welding device. The energy limiting unit comprises an energy comparing unit which is designed to compare the ignition energy value with a predetermined energy limit value. The energy limiting unit furthermore comprises a blocking unit which is designed to trigger an action in the event of which further ignition energy at the electrode is prevented in the time window. Furthermore the task is solved by a welding device which comprises a low-voltage source, wherein the low-voltage source is designed to generate low-voltage pulses on the low-voltage side, and comprises a conversion unit for converting the low-voltage pulses into high-voltage pulses which are applied on the high-voltage side for igniting the arc, and comprises an energy limiting unit according to the invention, wherein the blocking unit is designed to prevent further ignition energy occurring at the electrode in the time window by means of the action in the form of preventing further low-voltage pulses on the low-voltage side and / or high-voltage pulses on the high-voltage side and / or auxiliary voltage pulses on the high-voltage side in the time window. Preferably the energy limit value in the defined duration of time is in the range of 0.01 to 100 joule, preferably in the range of 0.1 to 10 joule, particularly preferably in the range of 0.5 to 5 joule. Furthermore an energy limit value of 4 joule / second can also be sought.

[0005] It is thus possible to ensure in the ignition operation and / or in the no-load operation and / or preferably in the welding operation that the ignition energy value present at the electrode does not exceed the energy limit value, whereby it is possible to prevent that a user of the welding device, if he comes into contact with the electrode or touches the electrode, suffers a dangerous or health-damaging electric shock during the ignition process. In contrast to the welding operation, it is likely during the ignition operation or the no-load operation that a welder comes into contact with the high-voltage pulses on the high-voltage side, since the high-voltage pulses are applied to the electrode of the welding torch, although an electric arc can not occur. In contrast, a direct contact of the welder with the low-voltage pulses on the low-voltage side is less likely, since the low-voltage pulses can only be touched within the welding device. In the case of the welding operation, the high-voltage pulses (and if necessary also the auxiliary voltage pulses, see below) occurring at the electrode are less dangerous for the welder, since the energy flows away almost completely through the workpiece and it is less likely that the welder reaches into the burning electric arc. Furthermore, it can also be desirable in certain cases to limit the energy in the welding operation, so that it is also possible in the welding operation to detect whether the ignition energy exceeds the energy limit value and, in the event of an excess, to trigger an action. The welding operation is understood to mean that an electric arc is maintained at least temporarily between the electrode and the workpiece, which introduces such a high energy into the workpiece or onto the workpiece surface that a melting of the workpiece surface, i.e. a change in the structure of the workpiece surface, or at least a general change in the workpiece surface occurs. Furthermore, the welding operation is understood to mean that energy is introduced into the workpiece with a power of more than 100 joules per second, more than 10 joules per second or more than 4 joules per second. Preferably, the electric arc is already burning during the welding operation, in contrast to which the electric arc is ignited in the ignition operation. The ignition operation is understood to mean that an ionization path is initially created between the electrode tip and the workpiece and / or an electric arc is initially created, and that after the electric arc has been extinguished, the ionization path is created again and / or the electric arc is created again between the electrode tip and the workpiece. Furthermore, the ignition operation is understood to mean that energy is introduced into the workpiece with a power of less than or equal to 4 joules per second and / or that energy is introduced into the gas path. The no-load operation describes the time between the welding device reaching the welding readiness state and the start of the ignition operation. The ignition energy value can be determined in a hardware unit and / or a software unit. The determination of the ignition energy value is preferably determined in a plurality of types in order to guarantee a high safety by means of redundancy.

[0006] Preferably, the high-voltage energy values of the high-voltage pulses are summed up during the time window; and the high-voltage energy values are used to determine the ignition energy value occurring at the electrode. This can be achieved, for example, by means of an integration of the high-voltage pulses occurring in the time window.

[0007] Furthermore, the energy value of the low-voltage pulses can be predetermined; and the high-voltage pulses occurring during the time window are counted and multiplied by the energy value of the low-voltage pulses in order to determine the high-voltage energy value aggregated during the time window. It is preferably assumed that the high-voltage energy value is equal to the ignition energy value (in particular if no auxiliary voltage pulses are provided, see below). The high-voltage pulses can be combined into a high-voltage pulse bundle, wherein the high-voltage pulses can have a duration of several nanoseconds to several microseconds. Thus, the total energy value of the low-voltage pulse bundle can be known and thus the total energy value of the high-voltage pulse bundle is known. Thus, the number of low-voltage pulse bundles during the time window can also be counted in order to determine the aggregated high-voltage energy value.

[0008] It is particularly advantageous that the low-voltage energy value of the low-voltage pulses is aggregated during the time window; and that this low-voltage energy value is used to determine the energy value occurring at the electrode. The low-voltage pulses comprise the same energy content as the associated high-voltage pulses in the same time interval (apart from losses, which can be estimated and / or calculated and / or constant). Thus, the high-voltage energy value applied at the electrode can be determined by measuring the low-voltage energy value occurring at the low-voltage side. Thus, the low-voltage energy value can be used to determine the ignition energy value. It is preferably assumed that the low-voltage energy value is equal to the ignition energy value (in particular if no auxiliary voltage pulses are provided, see below). The measurement of the low-voltage energy value on the low-voltage side is more cost-advantageous and less susceptible to disturbances than the measurement of the (equivalent) high-voltage energy value on the high-voltage side. The voltage of the high-voltage pulses can be in the range of 1 kilovolt to 50 kilovolts, for example approximately 10 kilovolts. The determination of the low-voltage energy value can be determined, for example, by integrating the low-voltage pulses in the time window.

[0009] Preferably, the energy value of the low-voltage pulses is predetermined; and the low-voltage pulses occurring during the time window are counted and multiplied by the energy value of the low-voltage pulses in order to determine the low-voltage energy value aggregated during the time window. Thus, the low-voltage energy value can be determined accurately during the time window.

[0010] In order to determine the low-voltage energy value, the energy value per time unit can also be predetermined for the low-voltage pulses. The time unit can be predetermined here as a physical unit for time measurement as seconds s, milliseconds ms or preferably microseconds μs. If the sum of the pulse durations of all low-voltage pulses occurring in the time window within the time window is known, in order to determine the low-voltage energy value in the time window, the sum of the pulse durations of the low-voltage pulses in the time window can be multiplied by the predetermined energy value per time unit. In order to determine the pulse duration of the low-voltage pulses, the pulse duration of each individual low-voltage pulse in the time window can be determined and thus determined or measured by software technology and / or hardware technology. The energy value per time unit can be specified here preferably in joules per microsecond.

[0011] If the plurality of high-voltage pulses is combined to a high-voltage pulse bundle, the low-voltage pulses can also be combined to a low-voltage pulse bundle accordingly. If the energy value of the low-voltage pulse bundle is known, the number of low-voltage pulse bundles can be counted during the time window in order to determine the low-voltage energy value summed up during the time window.

[0012] As an action, the generation of further low-voltage pulses and thus of high-voltage pulses can be blocked. To this end, the blocking unit can be designed to block the generation of further low-voltage pulses as an action. The blocking unit can be designed such that an active intervention into the pulse generation unit is made in order to block the generation of low-voltage pulses, which pulse generation unit is set up for generating low-voltage pulses and thus subsequently high-voltage pulses. It is thus ensured that no further low-voltage pulses occur in the time window. The same or different energy limit values for the ignition operation can be provided for the welding operation. Furthermore, the energy limit values for the ignition operation can be different energy limit values from the energy limit values for the no-load operation. Furthermore, a distinction can be made between actions to be triggered for the welding operation, the ignition operation and the no-load operation, wherein, by means of different actions, the occurrence of further ignition energy at the electrode is prevented in the time window respectively.

[0013] When the welding device is in the welding operation, the summation of the low-voltage energy values and / or the comparison with the low-voltage energy limit value and / or the triggering of the action can be deactivated. However, it can also be provided that the summation of the low-voltage energy values and / or the comparison with the low-voltage energy limit value and / or the triggering of the action is activated when the welding device is in the welding operation.

[0014] A detection unit can be provided, which is designed to distinguish between the welding operation of the welding device and the ignition operation and / or the no-load operation of the welding device and to deactivate the energy determination unit and / or the energy comparison unit and / or the blocking unit if necessary in the welding operation and to activate them if necessary in the ignition operation and / or the no-load operation.

[0015] The ignition or reignition of the arc is achieved by means of the high-voltage pulses generated at the electrode. After the ignition process has been achieved, the welding voltage is applied at the electrode, as a result of which the welding current flows. Since a high power output is desired during the welding process, the energy limitation can be deactivated in the welding operation.

[0016] By evaluating the through current, the total through current and / or the auxiliary through current, the different operating states of the welding device (welding operation, ignition operation, no-load operation,...) can be distinguished very quickly and accurately. Additionally, the evaluation can be implemented directly on the inverter assigned to the welding device, whereby the operating state can be recognized without additional delay and the safety function of the energy limitation unit can be activated immediately. By measuring the through current in the detection unit, the moment at which the arc achieves ignition can thus also be determined. The energy limitation of the overall system can thus be limited to the time of the safety-relevant moment. In contrast to a process current measurement and / or a process voltage measurement, which usually takes place outside the inverter, the direct current and / or voltage measurement in the inverter is significantly more advantageous in terms of the speed of the measurement, the evaluation of the measurement data and the susceptibility to interference of the measurement. The measurement in this form is therefore preferably also used for safety-critical and safety-relevant applications.

[0017] However, if the welding device is designed for alternating voltage welding, the welding current occurring at the electrode has a zero-crossing which preferably occurs periodically. In order to prevent the arc from extinguishing during the zero-crossing, an additional auxiliary voltage, in particular an auxiliary direct voltage, can be provided, which can be, for example, 200 to 300 V. In direct voltage welding, a zero-crossing in which the arc can extinguish does not usually occur during the welding process. The welding device is therefore designed in such a way that an auxiliary voltage pulse is not usually provided for direct voltage welding. The auxiliary voltage pulse is applied to the electrode of the welding torch like a high voltage pulse, whereby the auxiliary voltage pulse is also accessible to the welder during the ignition operation and / or the no-load operation.

[0018] In a multi-process welding device, which can handle more than just one welding process, such as the manual arc welding process (E-Hand-welding), the MIG / MAG welding process (metal inert gas welding / metal active gas welding) or the WIG welding process (tungsten inert gas welding), it is also conceivable to use an auxiliary voltage source for direct voltage welding. In this way, for example, the stability can be improved in the case of a process change, for example in the case of a change from direct voltage welding to alternating voltage welding. By using an auxiliary voltage source for direct voltage welding, the extinguishing of the arc can be suppressed in particular, but also in MIG / MAG welding.

[0019] Preferably, the auxiliary voltage pulses are introduced on the high voltage side in order to support the ignition of the arc; and the auxiliary voltage energy values of the auxiliary voltage pulses are summed up during the time window in order to determine an auxiliary voltage energy value, and the auxiliary voltage energy value is used to determine the ignition energy value occurring at the electrode. By the triggering action, further auxiliary voltage pulses are prevented in the time window.

[0020] In particular for AC voltage welding, a distinction can be made between ignition of the arc and maintenance of the arc at zero crossing in terms of the use of the auxiliary voltage pulse, in order to ensure that the limitation of the auxiliary voltage energy value takes place only in the safety-critical time window, i.e. during ignition and not during zero crossing.

[0021] In order to generate the auxiliary voltage pulse, the welding device can comprise at least one auxiliary voltage source. The auxiliary voltage pulse can improve ignition of the arc and is for example in the range of 100 V to 1 kV, preferably in the range of 200 V to 300 V. The auxiliary voltage pulse has a duration of several microseconds to several milliseconds.

[0022] Furthermore, the pulse duration of the auxiliary voltage pulse can be limited in software or hardware, so that the pulse duration of the auxiliary voltage pulse is for example a maximum of 40 μs in the ignition mode and / or a maximum of 600 μs in the welding mode.

[0023] If an auxiliary voltage pulse is provided, it is advantageous to determine the ignition energy value from the sum of the auxiliary voltage energy value and the high voltage energy value or from the sum of the auxiliary voltage energy value and the low voltage energy value.

[0024] The auxiliary voltage pulse can be temporally synchronized, preferably superimposed, with the high voltage pulse. Furthermore, the high voltage pulse can be temporally synchronized, preferably superimposed, with the auxiliary voltage pulse. This can advantageously contribute to the maintenance of the arc in the zero crossing of the welding current. For synchronization, a feedback signal can be used between the high frequency (HF) ignition unit and the auxiliary voltage source. This has the advantage that no voltage measurement is required for synchronization and thus no interfering variables or avoidable delays occur. The feedback signal can for example be generated at each actuation of the high frequency (HF) ignition unit and transmitted to the inverter and thus to the auxiliary voltage source. The inverter preferably knows the delay times of the recharging process of the high frequency (HF) ignition unit and also the operating times of the inverter itself and the delay times of the auxiliary voltage source and can thereby activate the auxiliary voltage source in synchronization with the high frequency pulse. Furthermore, the high voltage source can here again be activated in synchronization with the auxiliary voltage source. It is advantageous to take all delay times (print operating times, switching processes,...) into account in the generation of the high frequency pulse and in the generation of the auxiliary voltage pulse, until the respective voltage is actually applied to the electrode, in order to enable an exact synchronization. It is possible to activate the auxiliary voltage source depending on the application, so that the high frequency pulse can be positioned shortly before, shortly after or during the auxiliary voltage supply and the ignition characteristics can be optimized depending on the application.

[0025] It is possible to predetermine the energy value of the auxiliary voltage pulses, wherein the auxiliary voltage pulses occurring during the time window are counted and multiplied by the energy value of the auxiliary voltage pulses in order to determine the auxiliary voltage energy value aggregated during the time window. The auxiliary voltage energy value can also be determined by integrating the auxiliary voltage pulses in the time window.

[0026] Furthermore, for the auxiliary voltage pulses, it is possible, in order to calculate the auxiliary voltage energy value, to predetermine the energy value per time unit, for example also in J / μs. In order to determine the auxiliary voltage energy value transferred by the auxiliary voltage pulses, the pulse duration of a given auxiliary voltage pulse can be determined by software technology and / or hardware technology, and from this the sum of the pulse durations of the auxiliary voltage pulses occurring in the time window can be determined. The auxiliary voltage energy value transferred by the auxiliary voltage pulses in the time window can thus be calculated by multiplying the sum of the pulse durations of the auxiliary voltage pulses occurring in the time window by the predetermined energy value per time unit.

[0027] It is also possible to block the generation of further auxiliary voltage pulses in the time window as an action, for example in such a way that the auxiliary voltage source is deactivated.

[0028] It is also possible to determine a residual energy value in the time window from the difference between the energy limit value and the ignition energy value, and to determine from the residual energy value whether further auxiliary voltage pulses and / or high voltage pulses are to be prevented in the time window by the triggered action.

[0029] The aggregation of the auxiliary voltage energy value and / or the comparison with the auxiliary voltage energy limit value and / or the triggering of the further action can be deactivated when the welding device is in the welding operation.

[0030] The energy limiting unit can be embodied as a separate element, as an integral component of the welding device or as an integral component of a welding assembly, such as for example of an inverter or a high-frequency (HF) ignition unit. The energy determining unit(s) and / or the energy comparison unit(s) and / or the blocking unit(s) can be integral components of the energy limiting unit or distributed.

[0031] It is particularly advantageous to move the time window continuously, so that the end time is equal to the current time. The energy value of the low voltage pulses during the time window ending at the current time is thus determined continuously, i.e. the time window is looked back upon in a certain sense. This can be achieved in a simple manner by recording the low voltage pulses at least over the duration of the time window. A real-time measurement of the energy value per observation period is thus obtained. The observation period is preferably in the range of 0.01 to 60 seconds, preferably in the range of 0.25 to 5 seconds and particularly preferably in the range of 0.5 to 2 seconds. Furthermore, an observation period of 1 second can also be sought.

[0032] It is particularly advantageous to determine the ignition energy value currently occurring in the time window before the energy limit value is exceeded and to already block the generation of the low-voltage pulse and / or the auxiliary voltage pulse on the basis of the ignition energy value. It can thus be advantageous in the case of ignition energy values that are far from the energy limit value if it is sufficiently likely that the energy limit value is not reached even in the latter case, not to block further low-voltage pulses and auxiliary voltage pulses, but only the generation of the low-voltage pulse or the auxiliary voltage pulse. BRIEF DESCRIPTION OF DRAWINGS

[0033] The application is explained below with reference to the attached drawings, which show an exemplary, schematic and non-limiting advantageous design of the application. In the drawings: Figures la to 5d The application is explained below with reference to the attached drawings, which show an exemplary, schematic and non-limiting advantageous design of the application. In the drawings:

[0034] Figure la a schematic structure of an energy limiting unit, which comprises an energy comparison unit, an energy determination unit and a blocking unit is shown;

[0035] Figure lb a schematic structure of a high-frequency (HF) ignition unit with an energy limiting unit, which comprises a low-voltage energy determination unit is shown;

[0036] Figure lc a schematic structure of an auxiliary voltage source with an energy limiting unit of its own, which comprises an energy determination unit is shown;

[0037] Figure 2a a sequence of high-voltage pulses on the high-voltage side and a time window is shown;

[0038] Figure 2b an auxiliary voltage pulse occurring on the high-voltage side and a time window is shown;

[0039] Figure 2c a high-voltage pulse occurring on the high-voltage side and an auxiliary voltage pulse at least partially synchronized with the high-voltage pulse and a time window are shown;

[0040] Figure 3 two time windows in which an auxiliary voltage pulse and a high-voltage pulse, respectively, occur and in which the energy limit value is not exceeded, respectively, are shown;

[0041] Figure 4a a time window movable at a first point in time in which an auxiliary voltage pulse and a high-voltage pulse synchronized with one another occur and in which the energy limit value would be exceeded is shown;

[0042] Figure 4ba time window movable at a second time, in which the auxiliary voltage pulse and the mutually synchronized high voltage pulse occur and in which the energy limit value is not exceeded;

[0043] Figure 4c a time window movable at a third time, in which the auxiliary voltage pulse and the mutually synchronized high voltage pulse occur and in which the energy limit value will be exceeded;

[0044] Figure 5a a block diagram of a first embodiment of the invention is shown;

[0045] Figure 5b a block diagram of a second embodiment of the invention is shown;

[0046] Figure 5c a block diagram of a third embodiment of the invention is shown;

[0047] Figure 5d a schematic structure of a welding device is shown. DETAILED DESCRIPTION

[0048] In Figure la the welding device 100 shown schematically in comprises a low voltage source Q1 which is designed to generate a low voltage pulse P(U1) on a low voltage side 21. It can also be provided that the low voltage source Q1 generates a low voltage U1 and that the pulse generation unit 23 thus generates the low voltage pulse P(U1) from the low voltage U1 (not shown in Figure la The welding device 100 furthermore comprises a conversion unit 20 for converting the low voltage pulse P(U1) into a high voltage pulse P(U2) which is applied on a high voltage side 22 and which serves to ignite an arc arc between the electrode 17 and the workpiece W. In Figure la Furthermore, an energy limiting unit 5 according to the invention is provided in Figure la which comprises an energy determination unit 51, an energy comparison unit 52 and a blocking unit 53. The energy limiting unit 5 is connectable with the welding device 100 and is designed to determine an ignition energy value E occurring at the electrode 17 of the welding device during a time window T which extends from a start time Ta to an end time Te in an ignition operation of the welding device 100. The energy comparison unit 52 is designed to compare the ignition energy value E with a predetermined energy limit value G. The blocking unit 53 is designed to trigger an action A in the event of an exceeding of the energy limit value G in order to prevent a further ignition energy from occurring at the electrode 17 in the time window T. The determination of the ignition energy value E and the triggering of the action A are shown schematically in In the following figures exemplary embodiments are described in which the possibilities for determining the ignition energy value E and triggering the action A are described.

[0049] Figure lb An exemplary high-frequency (HF) ignition unit 3 for generating an electric arc arc is shown. In the high-frequency (HF) ignition unit 3 a conversion unit 20 is provided, which is designed essentially to convert a low voltage U1 (for example 24 V) applied on a low voltage side 21 into a high voltage U2 (for example 9.8 kV) applied on a high voltage side 22. For generating the low voltage U1 a low voltage source Q1 is provided on the low voltage side 21. Furthermore, a pulse generation unit 23 is provided, which generates a low voltage pulse P(U1) from the low voltage U1. This can be realized for example by a switch S, which is actuated by the pulse generation unit 23, as indicated in Figure lb . The low voltage pulse P(U1) occurring on the low voltage side 21 is converted onto the high voltage side 22 by means of the conversion unit 20, so that a high voltage pulse P(U2) is generated on the high voltage side 22. In the case of use of this high voltage pulse P(U2) an electric arc arc is ignited between the electrode 17 and the workpiece W during the ignition process.

[0050] Although the conversion unit 20 is shown in Figure lb only as a transformer with a primary winding on the low voltage side 21 and a secondary winding on the high voltage side 22, the conversion unit 20 can of course also comprise further elements, in particular further transformers. An input capacitor C1 is provided at the low voltage side 21 and an output capacitor C2 is provided at the high voltage side 22.

[0051] It is noted here that the low voltage energy value E1 output for generating the electric arc arc does not exceed a low voltage limit value G1 within the time window T. For this purpose, in accordance with the application an energy limitation unit 5 is provided. The energy limitation unit 5 comprises an energy determination unit 51, which is designed to determine the low voltage energy value E1 directed to the electrode 17 in the time window T extending from a start time Ta to an end time Te in the ignition operation or in the idle operation. Furthermore, the energy limitation unit 5 comprises an energy comparison unit 52, which is designed to compare the low voltage energy value E1 with a predetermined low voltage limit value G1. Furthermore, in the energy limitation unit 5 a blocking unit 53 is provided, which is designed to trigger an action A in the case of exceeding the low voltage limit value G1 in order to prevent the generation of further low voltage pulses P(U1) and of the thus converted high voltage pulses P(U2) during the time window T. In this way it is prevented that the low voltage energy value E1 is further increased during the time window T and exceeds the low voltage limit value G1.

[0052] In Figure lbIn particular, the energy determination unit 51 is advantageously designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21. Of course, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22. Furthermore, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21 and a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22. Figure lb In particular, the blocking unit 53 is exemplarily designed to access the pulse generation unit 23 in order to block the generation of further low voltage pulses P(U1).

[0053] The plurality of low voltage pulses P(U1) can be combined on the low voltage side 21 into a low voltage pulse bundle P1, respectively, and converted onto the high voltage side 22, so that a high voltage pulse bundle P2 with a plurality of high voltage pulses P(U2) occurs on the high voltage side 22. Figure 2a An exemplary (planned) sequence of the high voltage pulse bundle P2 is shown, which consists of the respective high voltage pulses P(U2) and the single high voltage pulse P(U2), which occurs on the high voltage side 22 after the conversion of the respective low voltage pulse bundle P1, which consists of the respective low voltage pulses P(U1) and the single low voltage pulse P(U1), respectively, during the ignition process. The high voltage pulse bundle P2 occurs, for example, with a frequency of 1 kHz to 100 kHz, and the high voltage pulses P(U2) occur, for example, with a frequency of 100 kHz to 10 MHz.

[0054] In particular, the energy determination unit 51 is advantageously designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21. Of course, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22. Furthermore, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21 and a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22. Figure lb In particular, the energy determination unit 51 is advantageously designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21. Of course, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22. Furthermore, it is also conceivable in another embodiment that the energy determination unit 51 is designed to determine a low voltage energy value E1 of the low voltage pulses P(U1) on the low voltage side 21 and a high voltage energy value E2 of the high voltage pulses P(U2) on the high voltage side 22.

[0055] Furthermore, an auxiliary voltage source 10 for generating an auxiliary voltage pulse P(U3) can be provided in the welding device 100, which can be additionally applied to the high voltage side 22. The auxiliary voltage pulse P(U3) can be used to improve the ignition of the electric arc arc.

[0056] Figure lcAn embodiment of the energy limiting unit 5 is shown, which incorporates an auxiliary voltage source 10 arranged on the welding transformer 7. In the auxiliary voltage source 10 there are two rectifiers R, which each have an upstream current-limiting resistor-capacitor combination for current limitation and each have a downstream capacitor for smoothing and energy storage. Two auxiliary pulse generation units 15 are provided, which are designed to operate each switch S for generating an auxiliary voltage pulse P(U3). In this embodiment, two rectifiers R are shown in the auxiliary voltage source 10, so that not only negative but also positive auxiliary voltage pulses P(U3) can be output. An energy determination unit 51 is located in the energy limiting unit 5 and is designed to determine an auxiliary voltage energy value E3 of the auxiliary voltage pulse P(U3) during the time window T in the ignition operation. This is achieved here by summing the auxiliary voltage pulses P(U3). If the ignition energy value E is generated exclusively by the auxiliary voltage pulses P(U3), then the ignition energy value E is equal to the auxiliary voltage energy value E3. The energy comparison unit 52 is designed to compare the auxiliary voltage energy value E3 with a predetermined auxiliary voltage limit value G3. The blocking unit 53 is designed to trigger an action A in the event of an excess of the auxiliary voltage limit value G3, in order to prevent further auxiliary voltage pulses P(U3) in the time window T, which is achieved here by accessing the auxiliary voltage source 10.

[0057] If a low voltage pulse P(U1) occurs in the time window T and thus a high voltage pulse P(U2) converted therefrom occurs and additionally an auxiliary voltage pulse P(U3), then the ignition energy value E can consist of the auxiliary voltage energy value E3 and the low voltage energy value E1 or of the auxiliary voltage energy value E3 and the high voltage energy value E2. This would correspond, for example, to a combination of the design solutions described in Figure lb and Figure lc .

[0058] The energy limiting unit 5 and / or the blocking unit 53 and / or the energy determining unit 51 and / or the energy comparing unit 52 can comprise a microprocessor-based hardware, for example a computer or a digital signal processor (DSP), on which a corresponding software for implementing the respective functions is executed. The energy limiting unit 5 and / or the blocking unit 53 and / or the energy determining unit 51 and / or the energy comparing unit 52 can also comprise an integrated circuit, for example an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA) or a configurable programmable logic device (CPLD), or be monitored with a microprocessor in parallel to the integrated circuit. The energy limiting unit 5 and / or the blocking unit 53 and / or the energy determining unit 51 and / or the energy comparing unit 52 can also comprise an analog circuit or an analog computer. A hybrid form is also conceivable. It is likewise possible that different functions are implemented on the same hardware and / or on different hardware parts. It is particularly advantageous in a hybrid form in which the individual units are implemented not only in hardware but also in software.

[0059] Figures 2a to 2c and 4a to 4c each represent a time window T, which starts at a time Ta and ends at a time Te. In Figure 3 Two time windows T1 and T2 are shown in As a value for the duration of the time window T, for example, 1 second can be assumed.

[0060] In Figure 2a In the time window T, three high-voltage pulse bundles P2 are exemplarily present, which each contain a high-voltage pulse P(U2). Since the high-voltage pulse bundles P2 are converted from the respective low-voltage pulse bundles P1, the same number of high-voltage pulse bundles P2 and thus also the same number of low-voltage pulses P(U1 ) as low-voltage pulse bundles P1 are provided in the time window T. The high-voltage pulse P(U2) thus contains a high-voltage energy value E2 in the time window T, which is equal to the low-voltage energy value E1 in the same time window T.

[0061] The number of low-voltage pulses P(U1 ) present in the time window T on the low-voltage side 21 can be determined, for example, by means of the energy determining unit 51 in Figure lbThe low-voltage energy value E1 is equal to the ignition energy value E if only the low-voltage pulses P(U1) and the high-voltage pulses P(U2) converted therefrom are provided but not the auxiliary voltage pulses P(U3). However, it is also possible to provide an energy determination unit 51 which counts the high-voltage pulses P(U2) occurring on the high-voltage side 22 in the time window T and multiplies this by the energy content (for example 1 joule) of the high-voltage pulses P(U2) in order to obtain a total high-voltage energy value E2 which is again equal to the ignition energy value E if only the low-voltage pulses P(U1) and the high-voltage pulses P(U2) converted therefrom are provided but not the auxiliary voltage pulses P(U3).

[0062] In Figure 2b The time window T comprises an exemplary (planned) sequence of auxiliary voltage pulses P(U3). The auxiliary voltage pulses P(U3) are directed onto the high-voltage side 22 during the ignition process. Four auxiliary voltage pulses P(U3) are exemplarily shown in the diagram in the time window T, which together contain an auxiliary voltage energy value E3.

[0063] The number of auxiliary voltage pulses P(U3) occurring in the time window T can be counted, for example, by means of Figure lc The auxiliary voltage energy determination unit 51 shown counts directly at the auxiliary voltage source 10 and multiplies this by the energy content (for example 1 joule) of the auxiliary voltage pulses P(U3) in order to obtain a total auxiliary voltage energy value E3. The auxiliary voltage energy value E3 is equal to the ignition energy value E if only the auxiliary voltage pulses P(U3) are provided but not the low-voltage pulses P(U1) and the high-voltage pulses P(U2) converted therefrom.

[0064] Figure 2c The combination of high-voltage pulses P(U2) and auxiliary voltage pulses P(U3) occurring on the high-voltage side 22 is shown. Furthermore, in Figure 2c The high-voltage pulses P(U2) are advantageously at least partially temporally synchronized with the auxiliary voltage pulses P(U3) in The synchronized application of high-voltage pulses P(U2) and auxiliary voltage pulses P(U3) is referred to as pulse combination K. Furthermore, the diagram shows four pulse combinations K, i.e. four high-voltage pulses P(U2) and four synchronized auxiliary voltage pulses P(U3), in the time window T. The pulse combinations K contain the ignition energy value E in the time window T, which is composed of the high-voltage energy value E2 (equal to the low-voltage energy value E1) and the auxiliary voltage energy value E3.

[0065] Furthermore, the energy determination unit 51 can also sum up the low voltage energy values E1 of the low voltage pulses P(U1) (or equivalently the high voltage energy values E2 of the high voltage pulses P(U2)) and separately sum up the auxiliary voltage energy values E3 of the auxiliary voltage pulses P(U3) in the time window T. This can also be implemented in separate energy determination units 51. The ignition energy value E is furthermore equal to the sum of the auxiliary voltage energy value E3 and the low voltage energy value E1 (or equivalently the high voltage energy value E2).

[0066] The summed energy value E is transferred to the energy comparison unit 52. In advance, an energy boundary value G of for example 4 Joule has been defined for a time window T of for example 1 second, which is also exemplarily defined. It is furthermore exemplarily assumed that the pulse combination K is equal to an energy value of 1 Joule. The comparison unit 52 determines for the time window T in Figure 2c that the ignition energy value E is equal to the energy boundary value G ("4 times 1" Joule), whereby the action A is not triggered. This means that no further high voltage pulse P(U2) and thus no further low voltage pulse P(U1) (and if necessary no further auxiliary voltage pulse P(U3)) is allowed in the current time window T. The energy comparison unit 52 therefore transmits the task of blocking said further pulses to the blocking unit 53. The blocking unit 53 triggers the respective action A. This can for example be implemented in the energy limiting unit 5 according to Figure lb or Figure lc in such a way that it directly acts on the pulse generation unit 23 and / or the auxiliary pulse generation unit 15.

[0067] A plurality of time windows T can be provided, wherein the summed low voltage energy values E1 of the contained low voltage pulses P(U1) (or pulse bundles PI) are compared to low voltage energy boundary values G1 during the individual time windows T, respectively. If necessary, the auxiliary voltage energy values E3 of the contained auxiliary voltage pulses P(U3) can furthermore be summed up and compared to auxiliary voltage energy boundary values G3 during the individual time windows T, respectively.

[0068] In the event of an excess of the energy boundary value G within the respective time window T, further high voltage pulses P(U2) and / or auxiliary voltage pulses P(U3) are blocked in the relevant time window T. The time windows T can be (at least partially) overlapping and / or arranged in succession. Different time windows T can furthermore be established for different use purposes, for example in order to record the energy introduced into the workpiece and for example at the same time to guarantee a safety-relevant function.

[0069] In the event of an excess of the energy boundary value G within the respective time window T, further high voltage pulses P(U2) and / or auxiliary voltage pulses P(U3) are blocked in the relevant time window T. The time windows T can be (at least partially) overlapping and / or arranged in succession. Different time windows T can furthermore be established for different use purposes, for example in order to record the energy introduced into the workpiece and for example at the same time to guarantee a safety-relevant function. Figure 3The first time window T1 and the second time window T2, which is merely exemplary adjacent to the first time window T1, are shown exemplary as time windows T. In the first time window T1 four auxiliary voltage pulses P(U3) and three high voltage pulses P(U2) occur. It can be concluded therefrom that in the first time window T1 three low voltage pulses P(U1) also occur. In the second time window T2, which is merely exemplary here directly adjacent to the first time window T1, likewise four auxiliary voltage pulses P(U3) and three high voltage pulses P(U2) occur. Under the assumption that the time windows T1 and T2 each last one second and that the pulse combination K of a high voltage pulse P(U2) and a synchronous auxiliary voltage pulse P(U3) has been assumed to be one joule, the ignition energy value E in both the first time window T1 and also in the second time window T2 will be below the energy limit value G of four joules. Therefore in neither of the two time windows T1 and T2 will the action A be triggered.

[0070] However, it is completely particularly advantageous if a time window T is provided which always ends at the current time and therefore runs with the current time. This means that the time window T moves to the right on the time axis t, so that at the current time the time window T always looks back in time, respectively in real time. The current time therefore always equals the end time Te. This can be achieved in that the time course of the high voltage pulses P(U2) and, if necessary, of the auxiliary voltage pulses P(U3) occurring is recorded at least over the period corresponding to the time window T.

[0071] If it is determined here that the energy limit value G has been reached in the time window T ending at the current time, the generation of further low voltage pulses P(U1) (and thus of further high voltage pulses P(U2)) and, if provided, of further auxiliary voltage pulses P(U3) is prevented until the low voltage pulses P(U1) (and thus the high voltage pulses P(U2)) and, if necessary, the auxiliary voltage pulses P(U3) have slid out of the time window T by the movement of the time window T, so that the ignition energy value E no longer reaches the energy limit value G in the time window T.

[0072] In Figures 4a to 4c the current time equals the end time Te and the time window T is considered to return to the start time Ta. Again, it is assumed that the pulse combination K consisting of a high voltage pulse P(U2) and a synchronous auxiliary voltage pulse P(U3) contains an energy value of one joule and that the energy limit value G equals four joules.

[0073] In Figure 4aFour pulse combinations K appear within time window T, thus not exceeding the energy boundary value G, but having already reached it. Because the energy boundary value G has been reached, at time Te, action A blocks the request for new pulse combinations K, and thus, as long as these four pulse combinations K are within time window T, no other pulse combinations K are generated. Time window T then continuously shifts to the right.

[0074] Figure 4b Showing about Figure 4a At a subsequent moment, the first pulse combination K has already slipped out of the time window T, and thus another pulse combination K has been generated within the time window T. Furthermore, the ungenerated pulse combination K... Figure 4b The image is also shown as a dashed line, where the cross again indicates that the pulse combination K is not included in the calculation of the ignition energy value E because no additional pulse combination K has been generated. Figure 4a As stated in [the text]. Therefore, in [the text] Figure 4b The ignition energy value E is equal to the energy boundary value G. This means that no other pulse combination K is allowed within the time window T until at least one other pulse combination K slips out of the time window T. Therefore, action A prevents another pulse combination K from appearing within the movable time window T. It should be noted that the previously blocked pulse combination K is also not counted in the determination of the ignition energy value E, because the pulse combination K was merely planned, but was actively prevented by action A, and therefore no energy is output to electrode 17.

[0075] exist Figure 4c In the middle, the time window T continues to slide to the right, where another pulse combination K will be set at the current end time Te. The pulse combination K, shown by the dashed line, is again blocked by the trigger action A (which is shown by the cross) to ensure that the ignition energy value E does not exceed the energy boundary value G.

[0076] Figure 5aA first exemplary embodiment of the application is shown. In the current source 1 there is in addition a process regulator 2, an internal high-frequency (HF) ignition unit 3, an internal inverter 4 with an auxiliary voltage source 10 and an energy limiting unit 5. The process regulator 2 is connected with the energy limiting unit 5, the high-frequency (HF) ignition unit 3 and the inverter 4 and thus with the auxiliary voltage source 10. The energy limiting unit 5 is additionally connected with the high-frequency (HF) ignition unit 3 and the inverter 4 and thus with the auxiliary voltage source 10. The internal high-frequency HF ignition unit 3 generates a low-voltage pulse P(U1), which is converted into a high-voltage pulse P(U2). For this purpose, the high-frequency (HF) ignition unit 3 can in addition comprise a low-voltage source Q1, a pulse generation unit 23 and a conversion unit 20, as described above. The inverter 4 with the integrated auxiliary voltage source 10 provides an auxiliary voltage pulse P(U3). The process regulator 2 requires a low-voltage pulse P(U1) in the high-frequency (HF) ignition unit 3 and an auxiliary voltage pulse P(U3) in the internal inverter 4 with the auxiliary voltage source 10 for igniting the arc arc. The high-voltage pulse P(U2) and the auxiliary voltage pulse P(U3) are combined and guided through the welding cable and through the welding torch SB to the electrode 17. Between the tip of the electrode 17 and the workpiece W the arc arc is ignited. In this embodiment there is a single energy limiting unit 5, which comprises an energy determining unit 51, an energy comparison unit 52 and a blocking unit 53, wherein the energy determining unit 51 sums up in a time window T an ignition energy value E consisting of a low-voltage energy value E1 of the low-voltage pulse P(U1) and an auxiliary voltage energy value E3 of the auxiliary voltage pulse P(U3). In the case of a desired energy limitation, i.e. in the case of a prevention of further ignition energy E in the time window T, this energy limitation should be achieved by the ignition energy value E exceeding an energy boundary value G, by the triggering of an action A blocking the low-voltage pulse P(U1) and thus the high-voltage pulse P(U2) and / or the auxiliary voltage pulse P(U3). It is also possible that the high-frequency (HF) ignition unit 3 and the inverter 4 are located outside the current source 1.

[0077] Figure 5bA second exemplary embodiment of the application is shown. In the current source 1 there are in addition a process regulator 2, an internal high-frequency (HF) ignition unit 3, an internal inverter 4 with an auxiliary voltage source 10 and two separate energy limiting units 5 which communicate with each other. The process regulator 2 is connected to the two energy limiting units 5, the high-frequency (HF) ignition unit 3 and the inverter 4 and thus to the auxiliary voltage source 10. The two energy limiting units 5 are coupled and additionally connected to the high-frequency (HF) ignition unit 3 and the inverter 4 and thus to the auxiliary voltage source 10. The internal high-frequency (HF) ignition unit 3 generates a low-voltage pulse P(U1) which is converted into a high-voltage pulse P(U2) and for this can in addition comprise a low-voltage source Q1, a pulse generation unit 23 and a conversion unit 20, as described above. The inverter 4 with the integrated auxiliary voltage source 10 provides an auxiliary voltage pulse P(U3). The process regulator 2 requires the low-voltage pulse P(U1) and / or the auxiliary voltage pulse P(U3) directly in the high-frequency (HF) ignition unit 3 and in the internal inverter 4 including the auxiliary voltage source 10 for igniting the arc arc. The high-voltage pulse P(U2) and the auxiliary voltage pulse P(U3) are combined and guided through the welding cable and through the welding torch SB to the electrode 17. The arc arc is ignited between the tip of the electrode 17 and the workpiece W. In this embodiment there are two energy limiting units 5 which communicate with each other, which together sum the ignition energy value E. The first energy limiting unit 5 sums the low-voltage energy value E1 of the low-voltage pulse P(U1) and the second energy limiting unit 5 sums the auxiliary voltage energy value E3 of the auxiliary voltage pulse P(U3). In addition, each of the two energy limiting units 5 or at least one energy limiting unit knows the total ignition energy value E, which represents the sum of the low-voltage energy value E1 and the auxiliary voltage energy value E3. In the event of an energy limitation due to the exceeding of the energy limit value G in the time window T, the low-voltage pulse P(U1) and thus the high-voltage pulse P(U2) and / or the auxiliary voltage pulse P(U3) are blocked by at least one energy limiting unit 5. Thus in this embodiment two energy limiting units 5 are shown which communicate with each other and jointly pay attention to the fact that the energy limit value G is not exceeded. In another embodiment it is also possible to provide two separate energy determination units 51 which jointly determine the ignition energy value E and communicate with each other, wherein in this other embodiment the ignition energy value E is compared to the energy limit value G in a central energy limiting unit 5. It is also possible that the high-frequency (HF) ignition unit 3 and / or the inverter 4 with the auxiliary voltage source 10 can be located outside the current source 1 with the respective energy limiting unit 5 or energy determination unit 51.

[0078] In addition, in Figure 5bIt is also possible that the first energy limiting unit 5 limits the low voltage energy value E1 to a first defined boundary value, for example, and the second energy limiting unit 5 limits the auxiliary voltage energy value E3 to a second defined boundary value, for example. The two boundary values can also be different here. The two internal energy limiting units 5 jointly limit the ignition energy value E to a third defined boundary value. The sum of the two boundary values is always kept below the previously defined energy boundary value G here.

[0079] Figure 5c A third exemplary embodiment of the application is shown. In the current source 1 there is in addition a process regulator 2 and an energy comparison unit 52 and an internal inverter 4 with an auxiliary voltage source 10 and an energy determination unit 51 and a blocking unit 53. Outside the current source 1 there is arranged an external high-frequency (HF) ignition unit 3 with its own energy determination unit 51 and its own blocking unit 53. The energy limiting unit 5 is implemented here in a distributed manner and thus comprises the energy comparison unit 52, the two energy determination units 51 and the two blocking units 53, as in Figure 5cThe energy limiting unit 5 is realized by connecting two energy determining units 51 with an energy comparison unit 52. The process regulator 2 is connected with the energy comparison unit 52 and thus with the energy limiting unit 5 consisting of internal and external components, the external high frequency (HF) ignition unit 3 and the inverter 4 and thus with the auxiliary voltage source 10. The external high frequency (HF) ignition unit 3 generates low voltage pulses P(U1) which are converted into high voltage pulses P(U2) and for this purpose can comprise a low voltage source Q1, a pulse generating unit 23 and a conversion unit 20 as described above. The internal inverter 4 with integrated auxiliary voltage source 10 provides auxiliary voltage pulses P(U3). The process regulator 2 requires low voltage pulses P(U1) and / or auxiliary voltage pulses P(U3) in the external high frequency (HF) ignition unit 3 and the internal inverter 4 with auxiliary voltage source 10 directly for igniting the arc arc. The high voltage pulses P(U2) and the auxiliary voltage pulses P(U3) are combined and guided through the welding cable and through the welding torch SB to the electrode 17. The arc arc is ignited between the tip of the electrode 17 and the workpiece W. In this embodiment there are two separate energy determining units 51 which communicate in the energy limiting unit 5, which add up the ignition energy value E. The first energy determining unit 51 adds up the low voltage energy value E1 of the low voltage pulses P(U1) and the second energy determining unit 51 adds up the auxiliary voltage energy value E3 of the auxiliary voltage pulses P(U3). The energy limiting unit 5 knows the total ignition energy value E which represents the sum of the low voltage energy value E1 and the auxiliary voltage energy value E3. In the case of an energy limitation in the time window T due to the exceeding of the energy boundary value G, further low voltage pulses P(U1) and thus high voltage pulses P(U2) and / or auxiliary voltage pulses P(U3) are blocked in the time window T by the blocking unit 53 by the action A.

[0080] The embodiments shown here represent only examples. In addition to the examples shown here, all combinations of inverter 4, auxiliary voltage source 10, internal or external arrangement, number of energy limiting units 5 and communication of energy limiting units 5 with each other, as well as different combinations of boundary values are possible.

[0081] Figure 5dAn electric circuit-technical implementation of a welding device 100 is shown, which has two identically communicating energy limitation units 5 according to the application. The welding device 100 comprises a current source 1, a welding torch SB and an electrode 17. The electrode 17 is located on one end of the welding torch SB, the second end of which is connected to the current source 1, and an arc arc is ignited between the electrode 17 and a workpiece W, which is likewise connected to the current source 1 via a ground connection. The current source 1 is connected on the input side to an electric power supply network AC LINE. The current source 1 comprises a process control unit or process regulator 2 with, for example, an integrated user interface 18, a high-frequency (HF) ignition unit 3, an inverter 4, two energy limitation units 5, a high-voltage conversion unit 6, a welding transformer 7, a no-load voltage increasing device 8, a secondary rectifier 9, an auxiliary voltage source 10, a polarity change unit 11, a primary power piece 12, a process voltage measuring device 13, a process current measuring device 14 and a probe unit 16. The exemplary high-frequency (HF) ignition unit 3 and the associated energy limitation unit 5 are shown in detail in Figure lb and the exemplary auxiliary voltage source 10 together with the associated energy limitation unit 5 are shown in detail in Figure lcis shown. Starting from the low frequency 50 / 60 Hz AC mains voltage (single or multi phase; 100 V to 600 V) of the electrical supply network AC LINE, this voltage is converted into a high frequency AC voltage (e.g. 1 kHz to several hundred kHz) by means of the primary power piece 12. The primary power piece 12 is connected with the process regulator 2 and this process regulator controls or regulates the energy flow. The converted high frequency AC voltage is provided on the primary winding side to the welding transformer 7 and this welding transformer converts this high frequency AC voltage onto the secondary winding side, which has a low voltage and high current intensity typical for the welding process. On the secondary winding side of the welding transformer 7 there is a secondary rectifier 9, which is implemented for example as a full-wave rectifier with intermediate tap and thus can provide a positive and negative output voltage. The secondary rectifier 9 is connected with the commutating unit 11 of the inverter 4 and provides the main current portion in the welding process. On the secondary winding side of the welding transformer 7 there is a no-load voltage increasing device 8. The no-load voltage increasing device 8 is connected in parallel to the secondary rectifier 9 and serves for increasing the no-load voltage from for example 60 V to 113 V. Likewise, the no-load voltage increasing device 8 can provide not only a positive but also a negative voltage. The no-load voltage increasing device 8 can provide support in case of an arc ignition, but since the coupled current limiting device provides only a limited current. Furthermore, the arc extinction can be prevented by the no-load voltage increasing device 8 to a certain extent. If the no-load voltage increasing device 8 is not sufficient, then the auxiliary voltage source 10 is switched on in order to prevent the arc extinction. On the secondary winding side of the welding transformer 7 there is additionally also the auxiliary voltage source 10, which is in turn located in the inverter 4. Furthermore, the auxiliary voltage source 10 and thus also the energy limiting unit 5 is connected with the commutating unit 11 by means of the detection unit 16. The commutating unit can comprise for example semiconductor transistors (such as insulated gate bipolar transistors (IGBT), metal oxide semiconductor field effect transistors (Mosfet), bipolar transistors, etc.). The commutating unit 11 switches the voltage originating from the no-load voltage increasing device 8 and / or the secondary rectifier 9 and / or the auxiliary voltage source 10 to the electrode 17 with the polarity predetermined by the process regulator 2. The detection unit 16 measures and recognizes the passage of the current and thus detects the welding run / no-load run / ignition run. In the inverter 4 there is the energy limiting unit 5, which is in turn connected with the auxiliary voltage source 10. This energy limiting unit 5 is basically connected with the Figure lcThe same applies to the embodiments shown in Fig. 2. For regulating the welding process, process voltage measuring means 13 and process current measuring means 14 are used by the process regulator 2. The process regulator 2 demands a high voltage pulse P(U2) in the high frequency (HF) ignition unit 3 and an auxiliary voltage pulse P(U3) in the inverter 4 for arc ignition or arc stabilization. In this embodiment, the high voltage pulse P(U2) of the high frequency (HF) ignition unit 3 is coupled into the welding circuit by means of a high voltage conversion unit 6. An energy limiting unit 5 for the high frequency (HF) ignition unit 3 communicates with the energy limiting unit 5 for the inverter 4 and is used for safety-critical ignition operation. A user interface 18 serves as an interface of the operator to the process regulator 2.

Claims

1. Method for safe operation of a welding device (100), wherein Converting low-voltage pulses (P(U1)) occurring on a low-voltage side (21) of a welding device (100) into high-voltage pulses (P(U2)) occurring on a high-voltage side (22) of the welding device (100), igniting an arc between an electrode (17) and a workpiece (W) during an ignition operation and / or a no-load operation using the high-voltage pulses (P(U2)), characterized in that a time window (T) is provided in the ignition operation and / or the no-load operation and / or the welding operation, which extends from a start time (Ta) to an end time (Te), during which the ignition energy value (E) occurring at the electrode (17) is determined and compared with an energy limit value (G), and in the event of an excess of the energy limit value (G), an action (A) is triggered in order to prevent further high-voltage pulses (P(U2)) in the time window (T).

2. The method of claim 1, wherein, The high-voltage energy value (E2) of the high-voltage pulses (P(U2)) is summed up during the time window (T); and this high-voltage energy value (E2) is used to determine the ignition energy value (E) occurring at the electrode.

3. The method of claim 2, wherein, The energy value of the high-voltage pulses (P(U2)) is predetermined; and the high-voltage pulses (P(U2)) occurring during the time window (T) are counted and multiplied by the energy value of the high-voltage pulses (P(U2)) in order to determine the high-voltage energy value (E2) summed up during the time window (T).

4. The method of claim 1, wherein, The low-voltage energy value (E1) of the low-voltage pulses (P(U1)) is summed up during the time window (T); and this low-voltage energy value (E1) is used to determine the ignition energy value (E) occurring at the electrode.

5. The method of claim 4, wherein, The energy value of the low-voltage pulses (P(U1)) is predetermined; and the low-voltage pulses (P(U1)) occurring during the time window (T) are counted and multiplied by the energy value of the low-voltage pulses (P(U1)) in order to determine the low-voltage energy value (E1) summed up during the time window (T).

6. The method of claim 4, wherein, The energy value of the low-voltage pulses (P(U1)) per time unit is predetermined; and the sum of the pulse durations of the low-voltage pulses (P(U1)) occurring during the time window (T) is determined, and this sum is multiplied by the energy value of the low-voltage pulses (P(U1)) per time unit in order to determine the low-voltage energy value (E1) summed up during the time window (T).

7. The method according to one of claims 1 to 6, characterized in that, An auxiliary voltage pulse (P(U3)) is introduced onto the high-voltage side (22) in order to support the ignition of the arc; and an auxiliary voltage energy value (E3) of the auxiliary voltage pulse (P(U3)) is summed up during the time window (T) in order to determine an auxiliary voltage energy value (E3) which is used to determine the ignition energy value (E) occurring at the electrode (17); and further auxiliary voltage pulses (P(U3)) are prevented by triggering an action (A) in the time window (T).

8. The method of claim 7, wherein, The auxiliary voltage pulses (P(U3)) are synchronized in time with the high-voltage pulses (P(U2)) or the high-voltage pulses (P(U2)) are synchronized in time with the auxiliary voltage pulses (P(U3)).

9. The method of claim 8, wherein, superimposing the auxiliary voltage pulses (P(U3)) on the high voltage pulses (P(U2)) or vice versa.

10. The method of claim 7, wherein, predetermining an energy value of the auxiliary voltage pulses (P(U3)); counting the auxiliary voltage pulses (P(U3)) occurring during the time window (T) and multiplying the energy value of the auxiliary voltage pulses (P(U3)) by the count in order to determine an auxiliary voltage energy value (E3) aggregated during the time window (T).

11. The method of claim 7, wherein, predetermining an energy value of the auxiliary voltage pulses (P(U3)) per time unit; determining the sum of the pulse durations of the auxiliary voltage pulses (P(U3)) occurring during the time window (T) and multiplying the sum by the energy value of the auxiliary voltage pulses (P(U3)) per time unit in order to determine an auxiliary voltage energy value (E3) aggregated during the time window (T).

12. The method of claim 7, wherein, determining a residual energy value from the difference between the energy limit value (G) and the ignition energy value (E) in the time window (T) and determining from the residual energy value whether further auxiliary voltage pulses (P(U3)) and / or high voltage pulses (P(U2)) are to be prevented by the action (A) triggered in the time window (T).

13. The method according to one of claims 1 to 6, characterized in that, continuously moving the time window (T) in real time such that the end time (Te) is equal to the current time.

14. The method of claim 7, wherein, blocking the generation of further low voltage pulses (P(U1)) and thus of high voltage pulses (P(U2)) and / or auxiliary voltage pulses (P(U3)) as the action (A).

15. The method according to one of claims 1 to 6, characterized in that, deactivating the triggering of the action (A) when the welding device (100) is in the welding mode.

16. Energy limiting unit (5) for a welding device (100) having a low voltage side (21) and a high voltage side (22), characterized in that The energy limiting unit (5) comprises at least one energy determining unit (51) designed to determine an ignition energy value (E) occurring at the electrode (17) during a time window (T) extending from a start time (Ta) to an end time (Te) in an ignition mode and / or in an idle mode and / or in a welding mode of the welding device (100); the energy limiting unit (5) comprises at least one energy comparison unit (52) designed to compare the ignition energy value (E) with a predetermined energy limit value (G); and the energy limiting unit (5) comprises at least one blocking unit (53) designed to trigger an action (A) in the event of an excess of the energy limit value (G) in order to prevent further ignition energy occurrences at the electrode (17) in the time window (T).

17. The energy limiting unit (5) according to claim 16, characterized in that There is provided a detection unit (16) designed to distinguish between a welding mode of the welding device (100) and an ignition mode and / or an idle mode of the welding device (100) and to deactivate the at least one energy determining unit (51) and / or the at least one energy comparison unit (52) and / or the at least one blocking unit (53) in the welding mode and to activate them in the ignition mode and / or in the idle mode.

18. A welding device (100) comprising: - a low-voltage source (Q1) designed to generate low-voltage pulses (P(U1)) on a low-voltage side (21), and comprising a conversion unit (20) for converting the low-voltage pulses (P(U1)) into high-voltage pulses (P(U2)) applied on a high-voltage side (22) for igniting an arc (arc) between an electrode (17) and a workpiece (W), and comprising at least one energy limitation unit (5) according to claim 16 or 17, wherein the blocking unit (53) is designed to prevent, by an action (A), the occurrence of further ignition energy at the electrode (17) in a time window (T) in such a way that further low-voltage pulses (P(U1)) on the low-voltage side (21) and / or high-voltage pulses (P(U2)) on the high-voltage side (22) and / or auxiliary voltage pulses (P(U3)) on the high-voltage side (22) are prevented.

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